Compounds that exhibit high-affinity binding to a voltage-dependent calcium channel subunit α2δ have been shown to be effective for treating, for example, neuropathic pain (see e.g., Non-Patent Documents 1 and 2). In this context, neuropathic pain refers to chronic pain caused by nervous tissue injury or the like and is a disease that significantly impairs quality of life to the extent that patients suffer from depression due to severe pain attacks.
Several types of α2δ ligands are currently known as therapeutic drugs for such neuropathic pain. Examples of α2δ ligands include gabapentine and pregabalin. α2δ ligands such as these compounds are useful for treating epilepsy and neuropathic pain or the like (e.g., Patent Document 1).
However, it has been reported that, for example, for gabapentine, its efficacy in the treatment of postherpetic neuralgia is approximately 60% according to patients' own evaluations (see e.g., Non-Patent Document 3) and that for pregabalin, its efficacy in the treatment of painful diabetic neuropathy is approximately 50% according to patients' own evaluations (see e.g., Non-Patent Document 4).
Other compounds are disclosed in, for example, Patent Documents 2, 3, and 4. However, the compounds disclosed in these Patent Documents are, principally, bicyclic saturated hydrocarbon compounds, which evidently differ from the compounds of the present invention.
Patent Document 1: Pamphlet of WO 04/006836
Patent Document 2: Pamphlet of WO 99/21824
Patent Document 3: Pamphlet of WO 01/28978
Patent Document 4: Pamphlet of WO 02/085839
Non-Patent Document 1: J. Biol. Chem. 271 (10): 5768-5776, 1996
Non-Patent Document 2: J. Med. Chem. 41: 1838-1845, 1998
Non-Patent Document 3: Acta Neurol. Scand. 101:359-371, 2000
Non-Patent Document 4: Drugs 64 (24): 2813-2820, 2004